1. Field of the Invention
The present invention pertains to a feed mechanism for driving document forms of indeterminate length through a printer platen and comprising spaced apart tractor mechanisms having cooperating sets of endless belts which provide improved bidirectional feeding and ease of loading the document into the tractor mechanisms.
2. Background Art
In the art of feeding documents into and out of various printer units, it is known to provide so-called tractor mechanisms which include endless drive belts having a series of lugs or pins which are adapted to engage spaced apart perforations along the opposed longitudinal sides of the document to provide positive feeding of the document with respect to the printer platen. There are also known document feed tractors which provide for bidirectional driving of the document while maintaining correct spacing of the printed lines and feeding of the document in and out of the platen. However, known types of bidirectional tractor mechanisms are difficult to load when the document is initially fed through the tractor mechanism to commence the feeding process.
For example, one known type of bidirectional tractor mechanism includes spaced apart frames on which endless drive belts are mounted and which include gates or guide members disposed adjacent the opposed longitudinal runs of the belts. The gates are pivotally mounted on the tractor mechanisms and are adapted to be opened for loading the document during the initial feeding of the document into the printer. However, the opposed openable gates are difficult to manipulate for proper loading of the document to assure that the document is engaged by the correct teeth or pins on the belts.
Accordingly, it has become highly desirable to provide improved document feed tractors which are easy to load without risk of damaging the document or inadvertently arranging the document with incorrect spacing with respect to the tractor drive belts. In the latter case, and with respect to the ease of loading of the documents, it is important that the document not be damaged by the tractor mechanism since, in many instances, the documents are serially numbered or have printed material already disposed thereon before being loaded into a particular printer. The present invention is directed to much needed improvements in document tractors which may be easily loaded and which provide bidirectional drive or feed capability.